Medical devices such as catheters, stents or balloons coated with drugs such as paclitaxel and sirolimus, tacrolimus or everolimus, are known. Frequently the drug is compounded with, or absorbed into, a polymer, or is absorbed into a porous material or is coated under a polymer. These techniques can provide for extended release of the drug, but they introduce complicating structural and biocompatibility issues.
Attempts to provide drug coatings that do not include polymers and that provide for extended release of the drug have presented skilled medical device designers with special difficulty.
The problem of providing a polymer-free drug coating specifically on stents is complicated in that a drug coating on the stent should survive expansion of the stent and remain in place until absorbed into tissue or dissolved into the bloodstream. Similar problems exist with other implanted medical devices that are left in the body for extended periods such as artificial heart valves, indwelling catheters, vascular grafts, vena cava filters, stent grafts and the like.
It is desirable however to have an drug coating comprising crystalline drug and at the same time utilizes no polymer. This is a problem because techniques for depositing drug directly on a substrate in crystalline form without a polymer produce very poor adhesion, and other techniques for depositing amorphous drug and then converting it to crystalline form, for instance as described in US 2010/0272773 and US 2011/0015664, commonly owned, and the latter proposes to nucleate the surface, however, the nucleating agent is taught as desirably one that is not soluble in the solvent used to apply the drug, which precludes using the drug itself as a nucleating agent. Water soluble substances are indicated to be preferable.